Improve w32notify notifications

* src/w32notify.c (DIRWATCH_BUFFER_SIZE): New macro.
(struct notification): 'terminate' is now a HANDLE.
(send_notifications): Argument is now a pointer to a
notification.  Don't loop waiting for the notification to be
acknowledged by the main thread; instead, just add the
notification to the linked list of notifications waiting to be
acknowledged.
(watch_end): Don't close the directory handle.
(watch_completion): Allocate a new notification structure to be
added to the notifications set.  Call ReadDirectoryChangesW
immediately after adding the new notification, and before sending
a message to the main thread about them.
(watch_worker): Don't loop calling ReadDirectoryChangesW; instead,
call it just once -- it will be called again in watch_completion.
Loop waiting for the main thread's indication to terminate.
(start_watching): Create the event to be used to indicate to the
worker thread that its should terminate.
(remove_watch): Indicate to the worker thread that it should
terminate.
* src/w32term.c (queue_notifications): Loop over all the
notifications in the linked list, processing all of them in one
go.
* src/w32inevt.c (handle_file_notifications): Loop over all the
notifications in the linked list.
* src/w32xfns.c (init_crit): Initialize the linked list of file
notifications.
(delete_crit): Free the linked list of file notifications,
including any unprocessed notifications left in it.
* src/w32term.h (struct notifications_se): New struct.

* test/lisp/filenotify-tests.el (file-notify-test02-events)
(file-notify-test05-dir-validity): Add read-event calls to
facilitate event recognition by the main thread in batch mode.

1 files changed, 176 insertions, 144 deletions

diff --git a/src/w32notify.c b/src/w32notify.c
index 586c2062f62..54d9bcc189a 100644
--- a/src/w32notify.c
+++ b/src/w32notify.c
@@ -22,27 +22,30 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 
    For each watch request, we launch a separate worker thread.  The
    worker thread runs the watch_worker function, which issues an
-   asynchronous call to ReadDirectoryChangesW, and then waits in
-   SleepEx for that call to complete.  Waiting in SleepEx puts the
-   thread in an "alertable" state, so it wakes up when either (a) the
-   call to ReadDirectoryChangesW completes, or (b) the main thread
-   instructs the worker thread to terminate by sending it an APC, see
-   below.
+   asynchronous call to ReadDirectoryChangesW, and then calls
+   WaitForSingleObjectEx to wait that an event be signaled
+   to terminate the thread.
+   Waiting with WaitForSingleObjectEx puts the thread in an
+   "alertable" state, so it wakes up when either (a) the call to
+   ReadDirectoryChangesW completes, or (b) the main thread instructs
+   the worker thread to terminate by signaling an event, see below.
 
    When the ReadDirectoryChangesW call completes, its completion
    routine watch_completion is automatically called.  watch_completion
-   stashes the received file events in a buffer used to communicate
-   them to the main thread (using a critical section, so that several
-   threads could use the same buffer), posts a special message,
-   WM_EMACS_FILENOTIFY, to the Emacs's message queue, and returns.
-   That causes the SleepEx function call inside watch_worker to
-   return, and watch_worker then issues another call to
-   ReadDirectoryChangesW.  (Except when it does not, see below.)
+   stashes the received file events in a linked list used to
+   communicate them to the main thread (using a critical section, so
+   that several threads could alter the same linked list), posts a
+   special message, WM_EMACS_FILENOTIFY, to the Emacs's message queue,
+   and returns.  That causes the WaitForSingleObjectEx function call
+   inside watch_worker to return, but the thread won't terminate until
+   the event telling to do so will be signaled.  The completion
+   routine issued another call to ReadDirectoryChangesW as quickly as
+   possible.  (Except when it does not, see below.)
 
    In a GUI session, the WM_EMACS_FILENOTIFY message posted to the
    message queue gets dispatched to the main Emacs window procedure,
    which queues it for processing by w32_read_socket.  When
-   w32_read_socket sees this message, it accesses the buffer with file
+   w32_read_socket sees this message, it accesses the linked list with file
    notifications (using a critical section), extracts the information,
    converts it to a series of FILE_NOTIFY_EVENT events, and stuffs
    them into the input event queue to be processed by keyboard.c input
@@ -53,7 +56,7 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
    procedures in console programs.  That message wakes up
    MsgWaitForMultipleObjects inside sys_select, which then signals to
    its caller that some keyboard input is available.  This causes
-   w32_console_read_socket to be called, which accesses the buffer
+   w32_console_read_socket to be called, which accesses the linked list
    with file notifications and stuffs them into the input event queue
    for keyboard.c to process.
 
@@ -62,24 +65,21 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
    bound to a command.  The default binding is file-notify-handle-event,
    defined on subr.el.
 
-   After w32_read_socket or w32_console_read_socket are done
-   processing the notifications, they reset a flag signaling to all
-   watch worker threads that the notifications buffer is available for
-   more input.
+   Routines w32_read_socket or w32_console_read_socket process notifications
+   sets as long as some are available.
 
    When the watch is removed by a call to w32notify-rm-watch, the main
-   thread requests that the worker thread terminates by queuing an APC
-   for the worker thread.  The APC specifies the watch_end function to
-   be called.  watch_end calls CancelIo on the outstanding
-   ReadDirectoryChangesW call and closes the handle on which the
-   watched directory was open.  When watch_end returns, the
-   watch_completion function is called one last time with the
-   ERROR_OPERATION_ABORTED status, which causes it to clean up and set
-   a flag telling watch_worker to exit without issuing another
-   ReadDirectoryChangesW call.  Since watch_worker is the thread
-   procedure of the worker thread, exiting it causes the thread to
-   exit.  The main thread waits for some time for the worker thread to
-   exit, and if it doesn't, terminates it forcibly.  */
+   thread requests that the worker thread terminates by signaling the
+   appropriate event and queuing an APC for the worker thread.  The
+   APC specifies the watch_end function to be called.  watch_end calls
+   CancelIo on the outstanding ReadDirectoryChangesW call.  When
+   watch_end returns, the watch_completion function is called one last
+   time with the ERROR_OPERATION_ABORTED status, which causes it to
+   clean up and set a flag telling watch_worker to exit without
+   issuing another ReadDirectoryChangesW call.  Since watch_worker is
+   the thread procedure of the worker thread, exiting it causes the
+   thread to exit.  The main thread waits for some time for the worker
+   thread to exit, and if it doesn't, terminates it forcibly.  */
 
 #include <stddef.h>
 #include <errno.h>
@@ -98,6 +98,7 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 #include "frame.h"      /* needed by termhooks.h */
 #include "termhooks.h"  /* for FILE_NOTIFY_EVENT */
 
+#define DIRWATCH_BUFFER_SIZE 16384
 #define DIRWATCH_SIGNATURE 0x01233210
 
 struct notification {
@@ -108,73 +109,52 @@ struct notification {
   char *watchee;        /* the file we are interested in, UTF-8 encoded */
   HANDLE dir;           /* handle to the watched directory */
   HANDLE thr;           /* handle to the thread that watches */
-  volatile int terminate; /* if non-zero, request for the thread to terminate */
+  HANDLE terminate;     /* event signaling the thread to terminate */
   unsigned signature;
 };
 
 /* Used for communicating notifications to the main thread.  */
-volatile int notification_buffer_in_use;
-BYTE file_notifications[16384];
-DWORD notifications_size;
-void *notifications_desc;
+struct notifications_set *notifications_set_head;
 
 static Lisp_Object watch_list;
 
 /* Signal to the main thread that we have file notifications for it to
    process.  */
 static void
-send_notifications (BYTE *info, DWORD info_size, void *desc,
-                    volatile int *terminate)
+send_notifications (struct notifications_set *ns)
 {
   int done = 0;
   struct frame *f = SELECTED_FRAME ();
 
-  /* A single buffer is used to communicate all notifications to the
-     main thread.  Since both the main thread and several watcher
-     threads could be active at the same time, we use a critical area
-     and an "in-use" flag to synchronize them.  A watcher thread can
-     only put its notifications in the buffer if it acquires the
-     critical area and finds the "in-use" flag reset.  The main thread
-     resets the flag after it is done processing notifications.
-
-     FIXME: is there a better way of dealing with this?  */
-  while (!done && !*terminate)
-    {
+  /* We add the current notification set to the linked list.  Use the
+     critical section to make sure only one thread will access the
+     linked list. */
       enter_crit ();
-      if (!notification_buffer_in_use)
-        {
-          if (info_size)
-            memcpy (file_notifications, info,
-                    min (info_size, sizeof (file_notifications)));
-          notifications_size = min (info_size, sizeof (file_notifications));
-          notifications_desc = desc;
-          /* If PostMessage fails, the message queue is full.  If that
-             happens, the last thing they will worry about is file
-             notifications.  So we effectively discard the
-             notification in that case.  */
-          if ((FRAME_TERMCAP_P (f)
-               /* We send the message to the main (a.k.a. "Lisp")
-                  thread, where it will wake up MsgWaitForMultipleObjects
-                  inside sys_select, causing it to report that there's
-                  some keyboard input available.  This will in turn cause
-                  w32_console_read_socket to be called, which will pick
-                  up the file notifications.  */
-               && PostThreadMessage (dwMainThreadId, WM_EMACS_FILENOTIFY, 0, 0))
-              || (FRAME_W32_P (f)
-                  && PostMessage (FRAME_W32_WINDOW (f),
-                                  WM_EMACS_FILENOTIFY, 0, 0))
-              /* When we are running in batch mode, there's no one to
-                 send a message, so we just signal the data is
-                 available and hope sys_select will be called soon and
-                 will read the data.  */
-              || (FRAME_INITIAL_P (f) && noninteractive))
-            notification_buffer_in_use = 1;
-          done = 1;
-        }
-      leave_crit ();
-      if (!done)
-        Sleep (5);
-    }
+  ns->next = notifications_set_head;
+  ns->prev = notifications_set_head->prev;
+  ns->prev->next = ns;
+  notifications_set_head->prev = ns;
+  leave_crit();
+
+  /* If PostMessage fails, the message queue is full.  If that
+     happens, the last thing they will worry about is file
+     notifications.  So we effectively discard the notification in
+     that case.  */
+  if (FRAME_TERMCAP_P (f))
+    /* We send the message to the main (a.k.a. "Lisp") thread, where
+       it will wake up MsgWaitForMultipleObjects inside sys_select,
+       causing it to report that there's some keyboard input
+       available.  This will in turn cause w32_console_read_socket to
+       be called, which will pick up the file notifications.  */
+    PostThreadMessage (dwMainThreadId, WM_EMACS_FILENOTIFY, 0, 0);
+  else if (FRAME_W32_P (f))
+    PostMessage (FRAME_W32_WINDOW (f),
+                 WM_EMACS_FILENOTIFY, 0, 0);
+  /* When we are running in batch mode, there's no one to send a
+     message, so we just signal the data is available and hope
+     sys_select will be called soon and will read the data.  */
+  else if (FRAME_INITIAL_P (f) && noninteractive)
+    ;
 }
 
 /* An APC routine to cancel outstanding directory watch.  Invoked by
@@ -188,10 +168,7 @@ watch_end (ULONG_PTR arg)
   HANDLE hdir = (HANDLE)arg;
 
   if (hdir && hdir != INVALID_HANDLE_VALUE)
-    {
-      CancelIo (hdir);
-      CloseHandle (hdir);
-    }
+    CancelIo (hdir);
 }
 
 /* A completion routine (a.k.a. "APC function") for handling events
@@ -202,13 +179,19 @@ VOID CALLBACK
 watch_completion (DWORD status, DWORD bytes_ret, OVERLAPPED *io_info)
 {
   struct notification *dirwatch;
+  DWORD _bytes;
+  struct notifications_set *ns = NULL;
+  BOOL terminate = FALSE;
 
   /* Who knows what happened?  Perhaps the OVERLAPPED structure was
      freed by someone already?  In any case, we cannot do anything
      with this request, so just punt and skip it.  FIXME: should we
      raise the 'terminate' flag in this case?  */
   if (!io_info)
-    return;
+    {
+      DebPrint(("watch_completion: io_info is null.\n"));
+      return;
+    }
 
   /* We have a pointer to our dirwatch structure conveniently stashed
      away in the hEvent member of the OVERLAPPED struct.  According to
@@ -216,26 +199,69 @@ watch_completion (DWORD status, DWORD bytes_ret, OVERLAPPED *io_info)
      of the OVERLAPPED structure is not used by the system, so you can
      use it yourself."  */
   dirwatch = (struct notification *)io_info->hEvent;
+
   if (status == ERROR_OPERATION_ABORTED)
     {
       /* We've been called because the main thread told us to issue
          CancelIo on the directory we watch, and watch_end did so.
-         The directory handle is already closed.  We should clean up
-         and exit, signaling to the thread worker routine not to
-         issue another call to ReadDirectoryChangesW.  Note that we
-         don't free the dirwatch object itself nor the memory consumed
-         by its buffers; this is done by the main thread in
-         remove_watch.  Calling malloc/free from a thread other than
-         the main thread is a no-no.  */
-      dirwatch->dir = NULL;
-      dirwatch->terminate = 1;
+         We must exit, without issuing another call to
+         ReadDirectoryChangesW. */
+      return;
     }
-  else
+
+  /* We allocate a new set of notifications to be linked to the linked
+     list of notifications set.  This will be processed by Emacs event
+     loop in the main thread.  We need to duplicate the notifications
+     buffer, but not the dirwatch structure.  */
+
+  /* Implementation note: In general, allocating memory in non-main
+     threads is a no-no in Emacs.  We certainly cannot call xmalloc
+     and friends, because it can longjmp when allocation fails, which
+     will crash Emacs because the jmp_buf is set up to a location on
+     the main thread's stack.  However, we can call 'malloc' directly,
+     since that is redirected to HeapAlloc that uses our private heap,
+     see w32heap.c, and that is thread-safe.  */
+  ns = malloc (sizeof(struct notifications_set));
+  if (ns)
+    {
+      memset (ns, 0, sizeof(struct notifications_set));
+      ns->notifications = malloc (bytes_ret);
+      if (ns->notifications)
+        {
+          memcpy (ns->notifications, dirwatch->buf, bytes_ret);
+          ns->size = bytes_ret;
+          ns->desc = dirwatch;
+        }
+      else
+        {
+          free (ns);
+          ns = NULL;
+        }
+    }
+  if (ns == NULL)
+    DebPrint(("Out of memory.  Notifications lost."));
+
+  /* Calling ReadDirectoryChangesW quickly to watch again for new
+     notifications.  */
+  if (!ReadDirectoryChangesW (dirwatch->dir, dirwatch->buf,
+                              DIRWATCH_BUFFER_SIZE, dirwatch->subtree,
+                              dirwatch->filter, &_bytes, dirwatch->io_info,
+                              watch_completion))
     {
-      /* Tell the main thread we have notifications for it.  */
-      send_notifications (dirwatch->buf, bytes_ret, dirwatch,
-                          &dirwatch->terminate);
+      DebPrint (("ReadDirectoryChangesW error: %lu\n", GetLastError ()));
+      /* If this call fails, it means that the directory is not
+         watchable any more.  We need to terminate the worker thread.
+         Still, we will wait until the current notifications have been
+         sent to the main thread.  */
+      terminate = TRUE;
     }
+
+  if (ns)
+    send_notifications(ns);
+
+  /* If we were asked to terminate the thread, then fire the event. */
+  if (terminate)
+    SetEvent(dirwatch->terminate);
 }
 
 /* Worker routine for the watch thread.  */
@@ -243,42 +269,43 @@ static DWORD WINAPI
 watch_worker (LPVOID arg)
 {
   struct notification *dirwatch = (struct notification *)arg;
+  BOOL bErr;
+  DWORD _bytes = 0;
+  DWORD status;
+
+  if (dirwatch->dir)
+    {
+      bErr = ReadDirectoryChangesW (dirwatch->dir, dirwatch->buf,
+                                    DIRWATCH_BUFFER_SIZE, dirwatch->subtree,
+                                    dirwatch->filter, &_bytes,
+                                    dirwatch->io_info, watch_completion);
+      if (!bErr)
+        {
+          DebPrint (("ReadDirectoryChangesW: %lu\n", GetLastError ()));
+          /* We cannot remove the dirwatch object from watch_list,
+             because we are in a separate thread.  For the same
+             reason, we also cannot free memory consumed by the
+             buffers allocated for the dirwatch object.  So we close
+             the directory handle, but do not free the object itself
+             or its buffers.  We also don't touch the signature.  This
+             way, remove_watch can still identify the object, remove
+             it, and free its memory.  */
+          CloseHandle (dirwatch->dir);
+          dirwatch->dir = NULL;
+          return 1;
+        }
+    }
 
   do {
-    BOOL status;
-    DWORD bytes_ret = 0;
-
-    if (dirwatch->dir)
-      {
-        status = ReadDirectoryChangesW (dirwatch->dir, dirwatch->buf, 16384,
-                                        dirwatch->subtree, dirwatch->filter,
-                                        &bytes_ret,
-                                        dirwatch->io_info, watch_completion);
-        if (!status)
-          {
-            DebPrint (("watch_worker, abnormal exit: %lu\n", GetLastError ()));
-            /* We cannot remove the dirwatch object from watch_list,
-               because we are in a separate thread.  For the same
-               reason, we also cannot free memory consumed by the
-               buffers allocated for the dirwatch object.  So we close
-               the directory handle, but do not free the object itself
-               or its buffers.  We also don't touch the signature.
-               This way, remove_watch can still identify the object,
-               remove it, and free its memory.  */
-            CloseHandle (dirwatch->dir);
-            dirwatch->dir = NULL;
-            return 1;
-          }
-      }
-    /* Sleep indefinitely until awoken by the I/O completion, which
-       could be either a change notification or a cancellation of the
-       watch.  */
-    SleepEx (INFINITE, TRUE);
-  } while (!dirwatch->terminate);
+    status = WaitForSingleObjectEx(dirwatch->terminate, INFINITE, TRUE);
+  } while (status == WAIT_IO_COMPLETION);
+
+  /* The thread is about to terminate, so we clean up the dir handle.  */
+  CloseHandle (dirwatch->dir);
+  dirwatch->dir = NULL;
 
   return 0;
 }
-
 /* Launch a thread to watch changes to FILE in a directory open on
    handle HDIR.  */
 static struct notification *
@@ -287,7 +314,7 @@ start_watching (const char *file, HANDLE hdir, BOOL subdirs, DWORD flags)
   struct notification *dirwatch = xzalloc (sizeof (struct notification));
 
   dirwatch->signature = DIRWATCH_SIGNATURE;
-  dirwatch->buf = xmalloc (16384);
+  dirwatch->buf = xmalloc (DIRWATCH_BUFFER_SIZE);
   dirwatch->io_info = xzalloc (sizeof(OVERLAPPED));
   /* Stash a pointer to dirwatch structure for use by the completion
      routine.  According to MSDN documentation of ReadDirectoryChangesW:
@@ -297,7 +324,9 @@ start_watching (const char *file, HANDLE hdir, BOOL subdirs, DWORD flags)
   dirwatch->subtree = subdirs;
   dirwatch->filter = flags;
   dirwatch->watchee = xstrdup (file);
-  dirwatch->terminate = 0;
+
+  dirwatch->terminate = CreateEvent(NULL, FALSE, FALSE, NULL);
+
   dirwatch->dir = hdir;
 
   /* See w32proc.c where it calls CreateThread for the story behind
@@ -307,11 +336,11 @@ start_watching (const char *file, HANDLE hdir, BOOL subdirs, DWORD flags)
 
   if (!dirwatch->thr)
     {
+      CloseHandle(dirwatch->terminate);
       xfree (dirwatch->buf);
       xfree (dirwatch->io_info);
       xfree (dirwatch->watchee);
       xfree (dirwatch);
-      dirwatch = NULL;
     }
   return dirwatch;
 }
@@ -370,7 +399,10 @@ add_watch (const char *parent_dir, const char *file, BOOL subdirs, DWORD flags)
     return NULL;
 
   if ((dirwatch = start_watching (file, hdir, subdirs, flags)) == NULL)
-    CloseHandle (hdir);
+    {
+      CloseHandle (hdir);
+      dirwatch->dir = NULL;
+    }
 
   return dirwatch;
 }
@@ -383,7 +415,7 @@ remove_watch (struct notification *dirwatch)
     {
       int i;
       BOOL status;
-      DWORD exit_code, err;
+      DWORD exit_code = 0, err;
 
       /* Only the thread that issued the outstanding I/O call can call
          CancelIo on it.  (CancelIoEx is available only since Vista.)
@@ -391,12 +423,10 @@ remove_watch (struct notification *dirwatch)
          to terminate.  */
       if (!QueueUserAPC (watch_end, dirwatch->thr, (ULONG_PTR)dirwatch->dir))
         DebPrint (("QueueUserAPC failed (%lu)!\n", GetLastError ()));
-      /* We also set the terminate flag, for when the thread is
-         waiting on the critical section that never gets acquired.
-         FIXME: is there a cleaner method?  Using SleepEx there is a
-         no-no, as that will lead to recursive APC invocations and
-         stack overflow.  */
-      dirwatch->terminate = 1;
+
+      /* We also signal the thread that it can terminate.  */
+      SetEvent(dirwatch->terminate);
+
       /* Wait for the thread to exit.  FIXME: is there a better method
          that is not overly complex?  */
       for (i = 0; i < 50; i++)
@@ -406,11 +436,13 @@ remove_watch (struct notification *dirwatch)
             break;
           Sleep (10);
         }
+
       if ((status == FALSE && (err = GetLastError ()) == ERROR_INVALID_HANDLE)
           || exit_code == STILL_ACTIVE)
         {
           if (!(status == FALSE && err == ERROR_INVALID_HANDLE))
             {
+              DebPrint(("Forcing thread termination.\n"));
               TerminateThread (dirwatch->thr, 0);
               if (dirwatch->dir)
                 CloseHandle (dirwatch->dir);
@@ -423,11 +455,11 @@ remove_watch (struct notification *dirwatch)
           CloseHandle (dirwatch->thr);
           dirwatch->thr = NULL;
         }
+      CloseHandle(dirwatch->terminate);
       xfree (dirwatch->buf);
       xfree (dirwatch->io_info);
       xfree (dirwatch->watchee);
       xfree (dirwatch);
-
       return 0;
     }
   else